Semiconductor laser devices as described above are generally known and widely used in many applications in a variety of industries, such as for example telecommunications industry.
Today's trend in optical communications is towards extending the optical fiber network to the end user (private or business) in order to provide a broad range of services, such as telephone, television and broadband internet. Therefore, the largest growth figures in optical communication networks are expected in the access network, where large numbers of local users get direct or wireless access to the optical network. Such effort to provide local users with direct optical access is known in jargon as Fiber To The Premises (FTTP) or Fiber To The Home (FTTH).
For large-scale application in telecommunication access networks light sources have to be simple, robust and low-cost. FTTH/FTTP requires a large volume of optical sources and therefore it will open a worldwide market for low-cost tunable lasers. A successful device for FTTH applications is a cheap, easy-tunable laser which operates in a small number of channels (4-8 wavelengths). In a larger area network such as a metropolitan or regional network, a successful device requires a higher performance operation in a larger number of channels (16-32 wavelengths).
Today's tunable sources usually consist of an optical laser cavity that can resonate at a large number of wavelengths. Two or three tunable elements inside the cavity are used for selecting the right wavelength out of a multitude. The relation between wavelength and control currents is complicated, and a complex control algorithm is needed for getting stable operation at the right wavelength. To provide the algorithm with the proper control data an extensive and expensive characterization of each laser is necessary.
It is an object of the present invention to provide a low-cost, robust light source, usable in a variety of optical communications solutions within the telecommunications industry.
It is a further object to overcome the abovementioned disadvantages and problems encountered with prior art light sources.
The invention thereto provides a semiconductor laser device comprising a first resonator section for resonating an optical resonator signal for providing an optical output signal at an output of said laser device, wherein said first resonator section is arranged for selectively resonating at a plurality of discrete output wavelengths, and wherein said laser device further comprises a second resonator section operatively connected to said first resonator section, said second resonator section being arranged for providing an optical feedback signal at a feedback wavelength to said first resonator section for locking said first resonator section into resonating at a selected output wavelength of said discrete output wavelengths, which selected output wavelength corresponds to said feedback wavelength for providing said optical output signal.
Proposed is a tuning approach in which a laser is used that can operate only at a discrete set of equally spaced wavelengths that are matched to the internationally standardized telecommunication wavelengths (ITU-grid). The desired wavelength is selected by re-injecting a small signal at the right wavelength into the laser (filtered feedback). For this purpose a compact active discretely tunable filter (Arrayed waveguide grating (AWG)) is used. This approach yields a better stability and a simpler tuning algorithm than the schemes that are presently applied.
For the wavelength-stabilization scheme the concept of Filtered Optical Feedback (FOF) may be applied, in combination with mathematical discoveries in the field of Delayed Differential Equations (DDE). As a control scheme, filtered feedback performs better than prior art solutions.
The laser and the feedback filter may be integrated in a small chip (<1 mm2) that can address a moderate number of wavelengths (8 or 16). This will provide a low-cost solution for large scale application in user access networks. For application in higher level networks more wavelengths are needed. The number of wavelengths of the chip may in accordance with an embodiment be extended by including a tunable Bragg reflector in the active filter, which enables to increase the total number of wavelengths with a factor of 2-4.
The description and claims at various locations make use of the wording ‘discrete wavelengths’. This is to be interpreted in line with the normal physical meaning thereof, i.e. not only comprising the exact wavelengths but rather comprising the mentioned wavelength and a narrow range around that wavelength, dependent on the characteristics of the elements to which the terminology applies.
Preferred and alternative embodiments are described in the dependent claims of the application.